Method for the regeneration of water-resistant paper as well as a method for the manufacture of paper from the material obtained and the sheets and webs of paper thus obtained



United States Patent US. Cl. 1625 4 Claims ABSTRACT OF THE DISCLOSURE In the regeneration of water-resistant paper, treating the paper at an elevated temperature with an aqueous solution of an organic aliphatic or aromatic compound containing at least one basic amino group in addition to at least one acidic group selected from the class consisting of carboxylic acid group and sulphonic acid group.

This invention relates to a method for the regeneration of water-resistant papers, as well as to a method for the manufacture of paper from the material obtained and the sheets and webs of paper thus obtained, in particular to the regeneration of papers which have been made water-resistant by means of urea-formaldehyde resin, melamine-formaldehyde resin and similar synthetic agents. Examples of such water-resistant papers are: towels, maps, paper for labels and phototype papers.

As regards the regeneration of such papers it is knOWn to digest these by means of an acidic hydrolysis. For this purpose rather strong acids or strongly acid agents, such as aluminium sulphate, are mostly used, sulphuric acid being a known agent and also the strong sulfamic acid NH SO H.

In the regeneration of old water-resistant paper with the aid of all agents known so far the aggressiveness of the agents used with respect to the cellulose fibre itself and with respect to the metal equipment always means a serious drawback. It is known operating in acid-proof apparatuses entails many inconveniences. These apparatuses are very expensive and it is often difficult to obtain them in the required shape and dimension. As has also been proposed to minimize the corrosion of the metal parts of the equipment by means of the addition of inhibitors. Various amines and imines are known as inhibitors. However, the use of all these inhibitors presents considerable drawbacks.

In order to obtain a satisfactorily protective action mostly rather strong concentrations are required, which is expensive, and yet often a certain corrosion continues to occur which cannot be neglected. Also the correct dosage and mixing of the inhibitors requires extra efforts and attention.

The invention provides a method in which the abovementioned drawbacks are avoided and according to which a favourable digestion of the water-resistant paper is accomplished with a minimum of corrosion of equipment and deterioration of fibre. The material obtained according to the method of the invention is at once suitable for being processed to paper.

The method according to the invention comprises the use as an acidic agent for the hydrolysis of one organic compound of the class of aliphatic and aromatic compounds containing in the molecule in addition to at least one acid reacting group also at least one group having anticorrosive properties.

For the method according to the invention the organic 3,438,851 Patented Apr. 15, 1969 compounds containing in addition to an acid reacting group also a NH -group have been found to be particularly suitable.

Although the invention is by no means restricted to the following compounds, as examples of aliphatic compounds which may be considered there may be mentioned glutamic acid, HOOCCH CH CHNH COOH, glycocoll, NH CH COOH and compounds with molecules having straight or branched carbon chains with at least one free NH -group and at least one free SO H-gI'Oup in the molecule. As aromatic compounds there may be mentioned the naphthylamine-sulphonic acids C1QH5(NH2) and C10H4(NH2) (SO3H)3, the S3- lection of the total of 43 isomers depending on the possibility of obtaining one specific isomer easier than another one and being also defined by the desired colour of the final product.

It is preferred to use in the method according to the invention a sulphanilic acid NH C H SO H. Also in this case as regards the effect the use of all three isomers is possible.

Compounds like toluidine sulphonic acids may also be considered.

In general one uses of the acidic agent concentrations of between 1 and 5 g. per liter and herewith at a temperature of 60 C. and higher a satisfactory digestion is obtained. This means that when subsequently using conventional means of the paper manufacture a spot-free paper may be manufactured directly from the material thus obtained.

It was found that the corrosion of iron, determined as a loss of weight under comparable conditions, was considerably less with sulphanilic acid than when using sulphuric acid or aluminium sulphate with various inhibitors. It was also found that in general it is not necessary to use pure compounds and that the same result may be obtained when using technical grades.

Also a mixture of various ones of the afore-mentioned types of compound may, if necessary, be used with advantage.

EXAMPLE I 1500 l. of water and 10 kg. of crude non-ground sulphanilic acid were introduced into a spherical digester. The spherical digester was closed, heated with steam and rotated during 15 min. Thereafter the sulphanilic acid was dissolved and the spherical digester was opened. Subsequently 1350 kg. of waste paper labels, rendered waterresistant with urea-formaldehyde resin, and another 1500 l. of warm water were introduced into the boiler. After the spherical digester had been closed digestion took place at l20-130 C. After having been boiled during 1.5 hours the mass was suitable to be processed to a spot-free paper.

EXAMPLE II In a spherical digester 20 kg. of crude non-ground sulphanilic acid were dissolved during 15 min. in 3000 l. of water while heating by steam was applied. Thereafter 3000 kg. of waste paper, rendered water-resistant with ureaformaldehyde resin, were introduced into the spherical digester with another 3000 l. of water. The pH value of the liquid was 5.5, After 2.5 hours of boiling the mass was suitable to be processed to spot-free paper. The temperature at the digestion was l20l30 C.

EXAMPLE III In an Escher-Wyss Pulpmaster of 8 m. an amount of 20 kg. of raw sulphanilic acid was dissolved in 3000 l. of water, this being done in 15 min. while heating with steam. Thereafter 960 kg. of waste phototype paper, ren- EXAMPLE IV 30 kg. of crude sulphanilic acid were dissolved in 5000 l. of water at 80 C. in a hydra pulper of 16 m. Simultaneously a quantity of 1200 kg. of water-resistant phototype paper, rendered water-resistant partly with ureaformaldehyde resin and partly with melamine-formaldehyde resin, was introduced into the pulper and the amount of water was supplemented to 15000 1. This was done with return water of the thickening apparatus and this water had a pH value of 2.5. The pH value of the mass amounted to 4.4. After a period of 1 hour at 80 C. it was found that the mass, after having passed through the thickening apparatus and a mono-shaft disintegrator, was entirely spot-free. Subsequently to the regeneration the material obtained can always be processed in a manner known per se to sheets and webs of paper of very good quality.

EXAMPLE V 20 g. of old paper (from English ordnance maps), rendered water-resistant with melamine-formaldehyde, were soaked in l l. of water containing g. of glutamic acid with a pH value of 4.0 during 35 min. at 85 C. After having been stirred for 2 min. in a Kenwood mixer this paper was fairly well disintegrated and after a further heating of 30 min. at 85 C. and 2 min. stirring in the Kenwood mixer it was in a disintegrated and spot-free condition.

EXAMPLE VI 20 g. of old paper (from English ordnance maps), rendered water-resistant with melamine-formaldehyde, were soaked in 1 l. of water containing 2.5 g. of glutamic acid, with a pH value of 4.15 during 1 hour at 85 C. After having been stirred in the Kenwood mixer this paper was found to be in a disintegrated and spot-free condition.

EXAMPLE VII 20 g. of old paper (waste of phototype papers), rendered water-resistant with urea-formaldehyde, were soaked in 1 1. of water containing 5 g. of 1-naphthylamine-6- sulphonic acid (Cleves acid) with a pH value of 3.69 during 1 hour at 85 C. After having been stirred for 2 min. in the Kenwood mixer the substance obtained was of a slightly gray colour but was in a reasonably spot-free and disintegrated condition.

EXAMPLE VIII 20 g. of old paper (waste of phototype papers), rendered Water-resistant with urea-formaldehyde, were soaked in 1 l. of water containing 5 g. of 2-naphthy1 amine-l-sulphonic acid (Tobias acid) with a pH value of 4.32 during 1 hour at 85 C. After having been stirred for 2 min. in the Kenwood mixer the substance obtained was slightly grayish but reasonably spot-free and disintegrated.

EXAMPLE IX 20 g. of old paper (waste of phototype papers), rendered water-resistant with urea-formaldehyde, were soaked in 1 l. of Water containing 5 g. of 2,6-naphthylamine sulphonic acid (Bronners acid) with a pH value of 4.42 during 1 hour at C. After having been stirred for 2 min. in the Kenwood mixer the product obtained had a greenish-yellow colour but was reasonably well disintegrated.

EXAMPLE X 20 g. of old paper, rendered water-resistant with mel amine-formaldehyde, were soaked in 1 l. of water containing 5 g. of 1-naphthylamine-3,S-disulphonic acid with a pH value of 4.1 during 1 hour at 85 C. After having been stirred for 2 min. in the Kenwood mixer the substance obtained had assumed a rosy colour but it was well disintegrated.

Apart from the above examples on a technical scale it has been established among other things on the basis of many and detailed tests on a laboratory scale with various acidic agents containing the NH -group that even paper, rendered water-resistant with a high percentage of melamine-formaldehyde resin, such as waste from English ordnance maps, could be very satisfactorily processed with the method according to the invention.

I claim:

1. A method for the regeneration of Water-resistant paper, in particular paper containing a formaldehyde resin, comprising mixing the paper at an elevated tem-' perature with an aqueous solution of an organic aliphatic or aromatic compound containing at least one basic amino group in addition to at least one acidic group selected from the class consisting of carboxylic acid group, and sulphonic acid group, the pH of said solution being between about 2.5 and 5.5.

2. A method according to claim 1 wherein said compound is sulphanilic acid.

3. A method for the manufacture of paper wherein the paper fibers are obtained according to the process of claim 1.

4. Sheets and Webs of paper prepared according to the method of claim 3.

References Cited UNITED STATES PATENTS 2,872,313 2/1959 House 162-6 3,245,868 4/ 1966 Espenmil-ler 1624 FOREIGN PATENTS 587,109 4/ 1947 Great Britain.

HOWARD R. CAINE, Primary Examiner.

US. Cl. X.R. 162-75 

